


three hearts, one beat

by towokuwusatsuwu



Category: Kamen Rider Build
Genre: Anal Sex, Banjou tops and Sento helps idk what to tag this, Explicit Sexual Content, Feels, Fluff and Smut, M/M, Multi, Rough Kissing, Threesome - M/M/M, romantic sex
Language: English
Status: Completed
Published: 2019-06-28
Updated: 2019-06-28
Packaged: 2020-05-28 12:01:22
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,168
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19393705
Author URL: https://archiveofourown.org/users/towokuwusatsuwu/pseuds/towokuwusatsuwu
Summary: Sento and Ryuga are a perfect team. Kazumi is an additional and welcome piece aka Romantic reflections during an intimate act.





	three hearts, one beat

**Author's Note:**

  * For [NearlyBanjou](https://archiveofourown.org/users/NearlyBanjou/gifts).



Sento never thought about the logistics of sharing his bed with two other grown men.

The bed fits two people just fine, that much he knows. There were enough moments in the very beginning, he and Ryuga stubbornly refusing to sleep on the floor. Back to back because Ryuga lost Kasumi and struggled through the loss much on his own, letting the guilt and pain gnaw at his gut while Sento stared at the wall and wondered if he could have prevented it. He doesn’t remember what changed, really. He just remembers waking up with Ryuga’s arms around his middle and Ryuga’s hard chest pressed against his back.

It’s equally as hard to remember when he turned to face Ryuga for the first time. He remembers pressing his hand to Ryuga’s face, though. Remembers the warm and soft skin under his palm, remembers the way Ryuga smiled at him as he turned to kiss the cup of his palm, teeth whispering against his skin. A promise neither of them would touch for a while.

There were less clothes. Less layers. Skin to skin, hands grasping for each other, fingers splayed across each other’s backs. Grasping for something, maybe just for comfort in the beginning but eventually each other for sure. Sento let himself entertain the thought that nothing would come between them as the obstacles became harder to overcome, as they were pushed apart and clawed their way back together time and time again.

This makes it ironic that Sawatari Kazumi is between them now, in a sense.

“How do you feel?” His voice is husky, his fingers tracing down the side of Kazumi’s face. His skin is flushed and hot, a thin sheen of sweat making it glisten. He’s beautiful.

“L-loaded question,” Kazumi chokes out. His lower lip is swollen and bitten red in a desperate attempt to muffle himself. None of them are trying to wake the girls. “ _ Banjo. _ ”

“Hmm?” Ryuga’s voice is soft and lazy in his ear. One arm is wrapped around Kazumi’s hip, fingers spread across his bare stomach. He’s toned and fit from hard labor, and Ryuga’s fingers trace the dips and curves of his abdominal muscles. His other hand is out of view like this. “What? I’m just doing what you told me to do.”

“Fuck you,” Kazumi spits out, but there’s no venom in his voice. He’s half-smiling around it.

Sento leans in and kisses him. He wraps his hand around the back of Kazumi’s neck and kisses him long and slow, a calculated dance of lips and tongues that let Kazumi muffle a few needy moans against him. Sento swallows them down, tastes them, weighs their texture on his tongue and chases more of them. Kazumi is nothing but accommodating, letting Sento in. Trusting him in a way Sento would have thought impossible.

“That’s pretty,” Ryuga comments, and Kazumi makes a high-pitched noise against Sento’s mouth. His hand grips Sento’s wrist, spasming there. “Oh, I wonder if you’ll do that again.”

“Bastard.” Kazumi pants, flushed red across his cheekbones, eyes hazy. He’s lost in it, trying to hold himself above the surface of the water but failing. Sento kisses him on the end of his nose and smiles when Kazumi huffs and swats weakly at his chest.

The sheet is tangled around their knees, pushed away because of the heat of the season and the act itself. Ryuga is propped up on his elbow, and Sento can see the line of his arm and where it disappears behind Kazumi. He can see how it moves, too, a careful and measured rhythm. Ryuga is brash and obnoxious and bold but he’s careful like this, careful with Kazumi’s body and his trust and the promise to take care of him.

“Sento, get his leg,” he says, and his voice is deeper and throatier. His eyes are dark, pupils blown so wide that in the half-darkness of the room, Sento can’t see the bright friendly brown of his eyes anymore. “Wrap it around you. Need to change the angle.”

“Of course, partner.” Sento flashes him a smile and Ryuga leans over Kazumi to kiss him, a hard smack of their lips. He can feel Ryuga’s teeth, but for just a moment.

Kazumi makes a pitiful little noise between them. “You’re conspiring to kill me.”

“Not  _ kill _ you,” Sento reassures him, smoothing a hand down his thigh. He’s strong all the way through, muscles here that flex under Sento’s fingers when he digs his fingers into the flesh, draws Kazumi’s leg up and around his waist. The choked cry he gets when that changes how Kazumi feels Ryuga’s fingers is gratifying. “Conspiring, though? Yes.”

“It’s not so bad, is it, Kazumin?” Ryuga licks up the side of his neck and it’s  _ wicked _ and Kazumi makes a weak sound, tilting his head, giving that skin up if Ryuga wants it.

Sento is the one who takes the offer, trailing his lips from Kazumi’s, along his jaw and down his throat. He scrapes his teeth over the thin, sensitive skin and Kazumi’s leg tightens around his waist, an unspoken command.  _ Don’t you dare go anywhere. _

As if he could. As if he’d ever want to leave this place right now.

“Ease up, you’re tense.” Ryuga is so close to Sento’s ear when he says it; he looks up to see Ryuga whispering the words into Kazumi’s hair. “You’re getting tight. Breathe for me.”

“It’s kind of hard to just  _ relax, _ ” Kazumi mutters, but he exhales and goes soft between them just the same, and Sento realizes he can see what’s going on from this angle.

Ryuga’s arms aren’t just toned; they’re  _ strong. _ You can see the muscles in them flexing as he moves his fingers inside of Kazumi, cords of muscle standing out against his skin like he’s trying to flex for them. He twists his wrist a little and Kazumi bites down on Sento’s shoulder, muffling a cry there. His thigh twitches hard against Sento’s hip.

“There we go.” Ryuga looks up and he and Sento lock eyes. The electricity between the two of them is never less than it is now, never less than this potent. It feels like a current Sento can see, that if he touched it he’d feel the shock to his system, the single all the way up into the socket of his shoulder. Ryuga grins at him, and his teeth flash white. “Help me out, huh? I think he could take a little bit more than I’m giving him.”

“Where’d you put the lube?” Sento asks, and Ryuga’s grin turns predatory.

They have to do some negotiating for Sento to get his hands on the bottle without Ryuga dislodging one of his hands, and Kazumi complains until Ryuga does  _ something _ with his hand and cuts off all of his complaints in one squeaky moan. Sento slicks his fingers and slips his hand around Kazumi’s hip until it meets Ryuga’s own. Negotiating again, but Kazumi is quiet this time, his breathing hot and labored, puffing against Sento’s collarbone. One of his hands grips Sento’s ribs so tight it hurts, but Sento doesn’t care that much.

“Breathe, Kazumin,” Ryuga says, and Kazumi breathes.

Sento strokes slick fingers around his rim, stretched hot around the two fingers Ryuga already has inside of him. “Can you handle both of us?”

“Yeah, I’m good.” Kazumi’s eyes are closed, but he’s breathing as evenly and slowly as he can. Deep breaths that move his chest. Sento can see the silver glitter of a chain against his sun-kissed warm skin. “Just… Go slow or I’m going to die on both of you.”

“Good man.” Sento kisses him on the forehead and Kazumi smiles faintly at him.

He’s tight but there’s enough lube to make everything slick and slippery enough that adding a third finger to him isn’t impossible. Hot and smooth inside, the muscles contracting around Sento’s finger, but not tonight enough for him to think it’s hurting. That Kazumi is in pain. His fingers dig into Sento’s side but he stays calm for both of them. There is something especially intimate about feeling Ryuga’s fingers inside of Kazumi and beside his own, and Ryuga leans over to kiss him, mouth warm and wet and soft.

“Doesn’t he feel nice?” Ryuga asks against his mouth, and Kazumi shudders between them, wrapping his entire arm around Sento’s body. “Easy, though, he’s sensitive.”

“That’s preferable,” Sento admits. “Together now, Banjo.”

“Oh, fuck me,” Kazumi says, soft and breathless like he’s just now realized what they’re doing to him. He doesn’t ask them to stop. He just presses his face into Sento’s shoulder.

They go slow for him, their fingers twisting and thrusting together. Sento has to turn his hand just a bit to get the angle he wants, rubbing his thumb just behind Kazumi’s balls, pressing against the smooth bit of skin there as Ryuga massages his prostate. It’s an instant effect, Kazumi gripping him with panicky tightness, choked gasps while his head falls back. It must feel so good for him, having both of them touch him like this.

His hips thrust back on their fingers and Sento can feel how hard he is, his cock rubbing up against Sento’s stomach while he tries to control his body. He wants to follow their touch and their movements but Ryuga hushes him, tells him to lie still and let them take care of him. Sento brushes his hair back with his free hand, kisses him, licks a groan off of his tongue, and Kazumi snatches a handful of his hair and makes it harsh and messy.

“Believe me when I say I’m planning on it,” Ryuga says, and Kazumi smacks him on the shoulder while Ryuga just laughs and presses tighter against his back.

“Touch yourself,” Sento urges, murmuring the words right against Kazumi’s lips. “For me.”

Kazumi huffs a tuft of chestnut hair off of his forehead and drags his hand out of Sento’s hair and between their bodies, fingers wrapping around his cock. “Pushy scientist.”

“I’m a genius, remember. I know what I’m doing.” Sento would do it himself but his hand is occupied, and he makes a point of that when he squeezes just one more finger in.

That’s Kazumi’s limit from the way he wheezes, but it’s enough to work him open slowly. He needs it; Ryuga’s size is generous for most people, even people who enjoy it. But he’s not flinching away from them, his hand working languidly between his legs as he lets his eyes fall shut. Trusting them to take care of him, giving himself just an edge of pleasure more.

“That’s perfect, Kazumi,” Sento tells him, and Kazumi keens just barely. “ _ You’re _ perfect.”

“I know. You’re lucky to have me,” Kazumi just manages, smoothing his fingers over the head of his cock, smearing pre-come down his shaft to ease the strokes.

Ryuga nods, nuzzling into Kazumi’s hair. “Hell yeah. You think you’re ready for me?”

“No time like the present.” Kazumi looks back at him and Ryuga catches him by the jaw and kisses him. It’s messy, and Sento can see flashes of their tongues curling together, drawing the other closer while Ryuga carefully slides his fingers free. Sento gives Kazumi a minute to breathe and then does the same, reaching past him for Ryuga’s cock.

The first time Ryuga ever touched him like this, Sento was hesitant, bordering on terrified when his brain fully conceptualized just how big Ryuga is. It’s not the length that’s the problem but the width of it, the slow burning stretch if there isn’t enough preparation and lube to make up for it. The first time they tried it, both of them were embarrassed and flustered and Ryuga apologized at least thirty times. The second time, they knew what they were doing, and Sento left long red lines down his back that Sawa teased him about the next morning when Ryuga’s shirt rode up and she noticed one of them.

They don’t make the same mistake with Kazumi. They’ve made enough mistakes.

“Fuck, Sento.” The quality of Ryuga’s voice in bed is thrilling, leaving a trail of goosebumps up Sento’s spine as he strokes Ryuga’s cock, the velvety skin over the length of it. “Easy.”

“I’m helping,” he says, and there’s a smirk in his words that Ryuga mirrors with his lips.

He has to fumble for the lube where they’ve set it down so he can help properly, not missing the hypnotic little rolls of Ryuga’s hips while he fucks up into Sento’s loose fist. It’s familiar and easy for both of them; they’ve been here so many times before that putting Kazumi between them really hasn’t changed much for the two of them. It’s only taught them how to work the dynamic with their new partner between them.

And he  _ is _ their partner. It’s unspoken but it’s there in the way Kazumi mouths at Sento’s neck, the way Ryuga presses a kiss to the roundest part of Kazumi’s shoulder. He belongs here now. Maybe he was meant to slot between them just like this.

Sento doesn’t know how much he believes in destiny, but it is food for thought.

“You ready, Kazumin?” Ryuga asks, his voice just a little strained. He’s harder in Sento’s hand, the tip of his cock slicker than it was before Sento touched him.

“Mhm.” Kazumi’s lids are heavy. He looks sleepy if not for the way his breath hitches against Sento’s skin. “Go slow. I’m still not really used to it.”

“Of course. I’m not an animal.” Ryuga shifts closer to him and Sento props himself up on an elbow, not letting go of Ryuga. He’s the one, instead, who guides Ryuga inside, pressing the head of his cock against Kazumi’s rim. With one easy roll of his hips, Ryuga is inside of him.

Kazumi’s breath hitches and his hand stops moving. Sento lets go of Ryuga and wipes his hand on the sheets before touching Kazumi’s face, cupping his cheek. Kissing him softly and slowly to help distract him from the initial stretch, the intensity of it, the pressure. He whines softly but doesn’t flinch away, doesn’t try to distance himself from them.  _ Perfect. _

“You feel so good, Kazumi.” Ryuga cups his hip and squeezes, the tendons standing out in his forearm. He’s trying so hard to go slow, to be as gentle as Kazumi needs him to be.

“You’re doing good,” Sento praises him, their noses brushing together. He cups the back of Kazumi’s head and draws him in close, letting him take as much strength and security as he needs, smoothing his fingers down his spine. “Tell us if you need him to stop.”

“I’m okay.” His lips move against Sento’s slowly and clumsily, and Sento gives him the kisses he wants, soothing him as best he can while he Ryuga eases inside of him.

Ryuga bottoms out inside of him and presses up against him, and they just hold Kazumi while he adjusts to it. Sento kisses his forehead and whispers to him how good he’s doing, how much they adore him, how perfect he is because he’s better with words than Ryuga, who reassures through touches and caresses. He’s well taken care of between the two of them and Sento is glad for him and glad they have each other.

“You can move,” Kazumi breathes. “And if you don’t I’m going to fight you.”

“Well with a threat like that,” Ryuga teases, and one roll of his hips has Kazumi stuttering.

Sento likes watching the two of them together when they fight, both of them graceful and deadly in their own right. He likes Ryuga’s brutal force and Kazumi’s skill, and he likes the way they work as a team. He loves their banter, the gentleness and playfulness of it all and the way Kazumi laughs at Ryuga’s stupid jokes. And he likes watching them together now, Ryuga’s movements slow and measured and rhythmic while Kazumi gasps and moans and lets his head fall back on Ryuga’s shoulder, fumbling to grasp the hand on his hip.

The two of them are beautiful together and they’re his, and Sento loves them.

“Touch me,” Kazumi all but pleads with him, and Sento reaches out to do just that.

He has the dexterous fingers of an engineer and can wrap his hand around both of them, the friction drawing a soft hiss from his lips while Kazumi keens quietly. There’s enough lube and pre-come that it’s sticky and slick, loud wet noises around his fingers to go with the soft thud of Ryuga’s hips against Kazumi’s, the labored sounds of their breathing in the quiet darkness. And it just feels good, the heat of Kazumi’s flesh against his, the sight of him flushed and ravished and clinging to both of them.

They aren’t ever going to let him go. Sento has already decided that.

“‘m close.” Kazumi claws at his forearm and Sento laughs softly, though it’s broken up by a low moan of his own. He is, too. Watching them together makes his skin burn and his veins run with magma. They mean so much to him now. They’re so important to him.

“Are you going to come for us?” Sento squeezes around them both gently and Kazumi whines, and Sento can recognize the way Ryuga’s hips move just a little faster, the way his breathing is tighter and harsher. He’s close, too. “I want you to come for us, Kazumin.”

“Yeah. Yeah.” Kazumi’s grip on his arm tightens. It hurts, but not too much. Even if there are fingerprint-shaped bruises in the morning, Sento won’t care. “Fuck,  _ please _ —”

Ryuga squeezes his hip and  _ grinds _ and Kazumi lets out an intelligible little noise, spilling hot and wet over Sento’s fingers. He’s still making those pitiful little sounds when Sento comes seconds later or when Ryuga groans, body shuddering against Kazumi’s back.

“Oh, fuck.” Kazumi shoves his face into the pillow. He’s slick with sweat and lube and come, and Sento kisses him on the temple. The only part of his face still showing. “Fuck.”

Gently, Ryuga eases out. “Are you okay? We didn’t hurt you, did we?”

“No. No, I’m okay. You’ve got to do that again sometime soon.” Kazumi slowly picks his head out of the pillow and Sento kisses him and touches him with the and not covered in bodily fluids. “Love you,” he rasps out. His throat sounds ruined.

“We love you, too,” Ryuga mumbles, already dragging himself to his feet. Probably to go find whatever towels they have clean and can wipe themselves off with since three people squeezing into a shower is going to be impossible.

“We do,” Sento confirms, and Kazumi smiles up at him and flops back down on the mattress, trying to slow his breathing and his rapid heartbeat.

Sento lies curled up next to him until their breathing— and their hearts— are in sync.


End file.
